Since the advent of agriculture, crops have required a consistent supply of water for optimal growth and vegetative yield. Heavy clay soils have been shown to loose about 70% of trapped moisture through evaporation, while sandy soils loose 65% of moisture through gravitational leaching. To limit gravitation leaching, physical barriers, such as submerged asphalt or plastic sheets, have been used to retard leaching. While effective in reducing leaching, physical barriers also limit vegetative growth, due to physical constraints on the crops' root system. Additionally, physical barriers also introduce foreign materials that may exude materials into the soil, crops, and/or water table.
Issues with leaching extend beyond water loss, including loss of fertilizer chemicals. Leaching of fertilizers causes farmers to add extra chemicals, which washout into streams and ground water along with the leached fertilizer, before the chemicals may be used by the crops.
Currently, agriculture depends on simple soil wetting agents and surfactants that migrate through soil resulting in sub-optimal root zone moisture retention. Utilizing these wetting agents results in soil wetting that draws moisture through the soil, but does not concentrate in the root zone, resulting in sub-optimal moisture retention in the root zone, less efficient irrigation utilization and higher treatment/re-treatment levels. Other moisture retention materials and strategies include starches, perlite, absorbent pumice and mulches of various compositions. These materials and strategies, like the use of simple wetting agents, do not target moisture retention in the root zone.
Traditional soil surfactant technology employs simple APG technology that helps to move water throughout a soil area with no ability to add or support any moisture retention. The best result that can be expected by the current technology is that moisture introduced into dry soils can be moved with some limitations throughout the soil matrix for more even distribution of the said moisture. Water absorbent polymers have become more widely used to address water leaching. It is thought that the polymers act as water “banks” or “reservoirs” for use by the crops. For example, Salestrom (U.S. Pat. No. 5,303,663) uses water absorbant polymers tilled into the soil. Cordani (U.S. application Ser. No. 11/775,512) discloses water absorbent polymers that are sprayed onto soil to provide a water reservoir during drought and stressed, dry crops. Salestrom (U.S. Pat. No. 5,868,087) discloses an absorbent polymer that is tilled into the top six inches of soil, and swells with water to limit water travel through soil.
However, polymers can absorb about 200-400 times their weight, with recommended applications of 20 pounds per acre, providing a maximum water capacity of 4,000 pounds of water per acre, whereas an actively growing agricultural crop uses about 40,000 pounds of water per day. Polymer reservoirs were determined to constitute less than 2% of the retention in soil (Salestrom, U.S. Pat. No. 5,649,495). Conversely, six inches of saturated loam-type soil can hold about 400,000 pounds of water. As such, the goal of using polymers for water retention is flawed.
Accordingly, there continues to be a need for effective soil water management, including soil treatments that concentrate moisture in the root zone for maximizing plant growth while minimizing irrigation water consumption.